By installing Joomla locally you can learn how to use Joomla and also for testing purpose and experiment you first need to test locally, than publishing directly World wide web.
So for Joomla installation you need Apache and PHP. For sake of convenience just download latest version of XAMPP and Install in your computer. You can refer this tutorial to install XAMPP in you computer.
After installation, open Xampp control panel and create a database for Joomla from PhpMyAdmin.
After creating a database its time to connect Joomla with database for installation. So download Joomla from their official website and extract zip file into C:\xampp\htdocs\joomla .
Now open following URL in any browser to install Joomla.
It will be redirected to installation page from where you can Install Joomla.
#1 Select the language to use during the Joomla! installation and then click next.
#2 Now Joomla will check Pre-installation requirements. Click next to proceed.
#3 Now you will see GNU General Public License, click next to skip and proceed further.
#4 Enter database details and other requirements to configure Database and to connect it with Joomla.
#5 Now you will get FTP configuration page but as we are installing Joomla locally, there is no use of ftp you can skip this step.
#6 After skipping previous step you will now get main configuration page for site setting.You can add here your website name,admin user-id and passwords etc.
#7 Click next after entering all details to finish installation.You will get warning to remove installation directory for security reason,so go to C:\xampp\htdocs\joomla and delete or move Installation directory to proceed.
Now you can visit your site or admin section for testing or any purpose by visiting http://localhost/joomla/ and http://localhost/joomla/administrator/ respectively.